Abstract: Apparatus for measuring the temperature of workpieces, particularly semiconductor wafers, during their processing, including a head assembly having a head plate circumscribed by a raised rim for receiving the workpiece and for spacing it from the head plate to define an enclosed volume between the head plate, rim, and workpiece; a thermally-conductive member, e.g., an optical fiber, passing through the head assembly and having one end exposed to the enclosed volume such that it receives thermal radiation therefrom; and a thermal detector aligned with the opposite end of the thermally-conductive member for detecting the thermal radiation received by it from the enclosed volume and for converting same to an electrical signal representing a measurement of the temperature of the enclosed volume.